Stable-signal producing circuit employing zener diode clipper and temperature-stablelow-pass and single frequency rejection filters



July 13, 1965 F. F. CILYO STABLE-SIGNAL PRODUCING CIRCUIT EMPLOYING ZENER DIODE CLIPPER AND TEMPERATURE-STABLE LOW-PASS AND SINGLE FREQUENCY REJECTION FILTERS Filed April 26, 1962 LI m -m wfim Q Q vi "mi k,

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FRANK E 0/1. Y0 By gflu/ Attorney United States Patent STABLESEGNAL PRGDUCHNG ClRCUlT EM- PLOYENG ZENER DIGDE CLER PER AND TEMPERATURE-STABLE LQ'W-PAES AND SHNGLE FREQUENCY REEEQTKON FILTERS Frank F. Cilyo, Export, Pa assignor to United States Steel Corporation, a corporation of New Jersey Filed Apr. 26, 1962, Ser. No. $9,343 4 Claims. (Cl. 307-885) This invention relates to apparatus for providing a stable alternating current voltage and more particularly for providing such voltage from an unstable alternating current power source. For accurate operation many control systems require an A.C. signal which has an amplitude that remains constant for extended periods of time. The signals are ordinarily provided from a line source of A.C. power.

It is therefore an object of my invention to provide a circuit that provides from a line source of A.C. power a highly stable reference signal of any desired amplitude.

Another object is to provide such a signal which is phase synchronized with the line source and is sinusoidal at an extremely low harmonic content.

These and other objects will be more apparent after referring to the following specification and attached drawings, in which:

FIGURE 1 is a schematic wiring iagram of my invention;

FlGURE 2 shows the wave form at one stage;

FIGURE 3 shows the wave form at a second stage;

FIGURE 4 shows the wave forms at two closely spaced points; and

FIGURE 5 shows the final wave form produced.

Referring more particularly to the drawings reference numeral 2 indicates a transformer having a primary winding 2P and a secondary winding 28. The primary winding is connected to a line source of alternating current Ll, L2. The secondary 28 is connected to a temperature stable Zener diode clipper 4 which includes an adjustable balancing potentiometer 6 having its arm on connected to conventional Zener diodes 3 and 1d. The signal from the diode clipper 4 is connected to a temperature stable low pass filter 12 which includes resistors 14 and 16 connected in series to a standard single frequency rejection filter 18. A first temperature stable capacitor 20 is connected between resistors 14 and 16 to ground and a second temperature stable capacitor 22 is connected between resistor 16 and filter 18 to ground. The signal from filter 18 is connected to an operational amplifier 24 which includes a resistor 26 and an adjustable resistor 23 connected in series and an A.C. amplifier 30 connected in parallel with resistor 23. The output signal appears between wires 32 and 34, the latter of which is connected to ground.

In operation the A.C. power source L1, L2, which normally is 60 cycles per second, is used to provide the initiating voltage for the circuit and the transformer 2 serves to isolate this power source from the remaining components of the circuit by providing a signal of the proper amplitude for introduction to the remaining components. This signal A which appears across the secondary 28 is shown in FIGURE 2 and in one specific embodiment may have an amplitude of 150 volts. The signal from secondary 25 is fed to the clipper 4. By adjusting the arm 6:: of the potentiometer 6, compensation by way of resistance change may be made for the diodes 8 and it) to insure that a symmetrical clipping is achieved. Once the proper setting of the arm 6a is obtained for the particular diodes involved no further adjustment is needed. The diodes S and clip the input signal as shown in FIGURE 2 to obtain the square wave form B shown in FIGURE 3 which in one specific embodiment has an amplitude of 35 volts.

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Signal B is delivered to temperature stable low pass filter 12. The capacitors 2t) and 22 pass the high frequency components of the signal B to ground. Signal C passing to the filter 1% is distorted only by the third harmonic which is eliminated by the filter 18 without attenuating the fundamental harmonic of this signal so as to provide a low amplitude output signal D shown in FIGURE 4. In the particular example given the amplitude of this signal is only volt. This signal has an extremely pure wave form but its amplitude is too low for direct utilization as a reference signal for most applications. Thus the operational amplifier 24 amplifies this low level signal D to any desired level without affecting its pure wave form and amplitude stability. For example, in the particular example given the amplitude of output signal E is 5 volts. The amplitude of the output signal E may be increased by increasing the resistance of variable resistor 28. Thus a highly stable reference signal is obtained, the amplitude of which is not affected from the preset amplitude by changes in temperature. The amplitude of the reference signal will remain constant for long periods of time with the frequency of the signal corresponding to that of the line source.

While one embodiment of my invention has been shown and described, it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

I claim:

1. Apparatus for providing a stable alternating current voltage from an unstable alternating current power supply comprising a symmetrical clipper for removing the peak voltages from the power source signal, means for isolating the power source from said clipper, and a temperaturestable low-pass filter connected to the output of said clipper, said temperature-stable low-pass filter including two resistors connected in series to a single frequency-rejection filter, a first temperature-stable capacitor connected between said resistors to ground and a second temperature stable capacitor having one side connected between said single frequency-rejection filter and the resistor adjacent thereto and the other side connected to ground.

2. Apparatus for providing a stable alternating current voltage from an unstable alternating current power supply comprising a transformer having primary and secondary windings with the primary adapted to be connected to the power supply, a symmetrical diode clipper connected to said secondary winding, a temperature-stable low-pass filter connected to the output of said diode clipper, said temperature-stable low-pass filter including two resistors connected in series to a single frequency-rejection filter, a first temperature-stable capacitor connected between said resistors to ground and a second temperature-stable capacitor having one side connected between said single frequency-rejection filter and the resistor adjacent thereto and the other side connected to ground, and an operational amplifier connected to the output of said temperature-stable low-pass filter, said operational amplifier including a resistor and an adjustable resistor connected in series and an A.C. amplifier connected in parallel with said adjustable resistor.

3. Apparatus for providing a stable alternating current voltage from an unstable alternating current power supply comprising a symmetrical clipper for removing the peak voltage from the power source signal, said symmetrical clipper including a balancing potentiometer having an arm and two Zener diode clippers electrically connected one to each side of said arm, means for isolating the power source from said clipper, and a temperaturestable low-pass filter connected to the output of said diode clipper, said temperature-stable low-pass filter including two resistors connected in series to a single frequencyrejection filter, a first temperature-stable capacitor connected between said resistors to ground and a second temperature-stable capacitorthaving one side connected between said single frequency-rejection filter and the resistor adjacent thereto and the other side connected to ground.

4. Apparatus for providing a stable alternating current voltage from an unstable alternating current power supply comprising a transformer having primary and secondary windings with the primary adapted to be connected to the power supply, a symmetrical diode clipper connected to said secondary winding, said symmetrical clipper including a balancing potentiometer having an arm and two Zener diode clippers connected one to each side of said arm, a temperature-stable low-pass filter connected to the output of said diode clipper, said temperature-stable low-pass filter including two resistors connected in series to a single frequency-rejection filter, a first temperature-stable capacitor connected between said resistors to ground and a second temperature-stable capacitor having one side connected between said single frequency-rejection filter and the resistor adjacent thereto and the other side connected to ground, and an operational amplifier connected to the output of said temperature-stable low-pass filter, said operational amplifier including a resistor and an adjustable resistor connected in series and an AC. amplifier connected in parallel with said adjustable resistor.

References Cited by the Examiner UNITED STATES PATENTS 10 2,682,031 6/54 Pocock 33320 X 2,819,442 1/58 Goodrich 307-885 2,861,239 11/58 Gilbert 307-4585 OTHER REFERENCES 15 Radiotron Designers Handbook, fourth edition, published by the Wireless Press, 1953, page 196.

ARTHUR GAUSS, Primary Examiner.

2O GEORGE N. WESTBY, Examiner. 

1. APPARATUS FOR PROVIDING A STABLE ALTERNATING CURRENT VOLTAGE FROM AN UNSTABLE ALTERNATING CURRENT POWER SUPPLY COMPRISING A SYMMETRICAL CLIPPER FOR REMOVING THE PEAK VOLTAGES FROM THE POWER SOURCE SIGNAL, MEANS FOR ISOLATING THE POWER SOURCE FROM SAID CLIPPER, AND A TEMPERATURESTABLE LOW-PASS FILTER CONNECTED TO THE OUTPUT OF SAID CLIPPER, SAID TEMPERATURE-STABLE LOW-PASS FILTER INCLUDING TWO RESISTORS CONNECTED IN SERIES TO A SINGLE FREQUENCY-REJECTION 